This invention relates to the generation of electricity by thermoelectric conversion of heat from a local primary source and has particular relationship to nuclear heart pacers or pacemakers. To the extent that this invention has other uses than in heart pacers it is understood that such uses are within the scope of this application.
A nuclear heart pacer includes a primary source of radioactive material, a thermoelectric converter which converts the heat from the source into electricity, and an electrical circuit powered by the converter which converts the output of the thermoelectric converter into pulsations and controls the flow of the pulsations to the heart. The primary source is typically composed of plutonium 238 which emits alpha particles. Such particles have a short range but in passing through material the alpha particles produce X-rays which have a long range. The quantity of radioactive material which is used is usually sufficient to produce the power necessary for the pacer over a period of about 20 years. In accordance with the teachings of the prior art this quantity is between one-third and one-half gram of Pu.sub.238. It is desirable that this quantity of radioactive material be minimized both to minimize the hard X-rays and also because the cost of Pu.sub.238 is very high and at the same time to increase the useful life of the pacer and this is an object of this invention.
In accordance with the teachings of the prior art the thermoelectric converter is a thermopile formed of wires. It has been realized, in arriving at this invention, that the quantity of radioactive material may be reduced by replacing the wire thermopile with a thermoelectric unit of the solid-state type. However, in the use of the prior-art nuclear heart pacers, it was discovered that the normal physical activities of the person or animal, having a heart pacer, subject the pacer to relatively high mechanical shocks or impacts which damage the pacer. Solid-state thermoelectric elements are brittle and fragile and substantially incapable of withstanding tensile stress and a heart pacer having a solid-state thermoelectric unit may in a short time after installation be damaged as a result of the normal physical activities of the host.
It is an object of this invention to overcome these disadvantages and to provide a heart pacer having a solid-state thermoelectric unit in which the converter and other related components shall be protected from physical or mechanical shocks and impacts resulting from the normal activities of the host.